The invention relates to a vacuum switch of the type which is typically used as part of a circuit breaker.
More particularly, the invention relates to a vacuum switch which has a housing for a vacuum chamber, the housing including a metal cylinder and an insulating cylinder which are axially aligned and hermetically sealed at adjacent ends, as by a soldered flange. Opposite ends of the housing are closed by end plates. A stationary electrode and a movable electrode in the vacuum chamber are surrounded by the metal cylinder. Stationary and movable lead rods are fixed to the respective electrodes and project in opposite directions from the chamber through the respective end plates. A magnetic coil whose coil body surrounds the metal cylinder with a winding which is connected via an input terminal lead with the lead rod extending through the end plate closing the end of the metal cylinder and is connected via an output terminal lead with a connecting point adjacent the metal cylinder, for connection to other circuit elements. Such a switch is disclosed in European published patent application No. EP 0,241,814.A2 and is illustrated in FIG. 1.
The prior art interrupter switch shown in FIG. 1 has a vacuum envelope 1 in which disc-shaped stationary and movable electrodes 2 and 3 are disposed and operable for forming or interrupting electrical contact therebetween. The vacuum envelope 1 includes an insulating cylinder 4, a disc-shaped metal end wall or plate 5 hermetically secured to one edge of the insulating cylinder 4 via a metal seal ring 6, a metal cylinder 7 having a flat bottom wall 7a and an open end hermetically secured to the other edge of the insulating cylinder 4 via another metal seal ring 6'. The stationary and movable electrodes 2 and 3 are located within the metal cylinder 7.
A stationary lead rod 9 passes hermetically through, and is fixed to the flat bottom end wall 7a. An inner end of the stationary lead rod 9 carries the stationary electrode within the metal cylinder 7. On the other hand, a movable lead rod 10 passes loosely through the metal end plate 5 and is hermetically secured to the end plate 5 via a metal bellows 11. An inner end of the movable lead rod 10 carries the movable electrode 3 within the metal cylinder 7.
A sharp-edged, uniformly thin-walled coil 13 of substantially one turn surrounds the stationary and movable electrodes 2 and 3 outside the metal cylinder 7. The coil 13 produces an axial magnetic field running parallel to the arc current path between the separated stationary and movable electrodes 2 and 3 for dispersing the arc evenly across the opposing faces of the electrodes, thereby increasing the current interruption performance of the interrupter switch. One end 13a of the coil 13 is electrically connected by a radially extending terminal lead (not shown in FIG. 1) to an outer end of the stationary lead rod 9. The other end 13b of the coil 13 is electrically connected by another radially extending terminal lead (not shown in FIG. 1) to one end of an outer lead rod 14 which is located outside of the vacuum envelope 1. An outer lead rod 15, also located outside the vacuum envelope 1, has a slide contact 16 at one end which mechanically and electrically engages an outer end of the movable lead rod 10.
In operation, an operating current (e.g. a fault current) passes through the sequence comprising the outer lead rod 14, one terminal lead (not shown), the coil 13, the other terminal lead (not shown), the stationary lead rod 9, the stationary electrode 2, the arc current path between the stationary electrode 2 and the movable electrode 3, the movable electrode 3, the movable lead rod 10, the slide contact 16 and the outer lead rod 15, and vice versa.
Such prior art switches are disadvantageous for dissipating the heat from the vacuum switching chamber since the sharp-edged cylindrical, uniformly thin-walled shape of the coil itself and long radially extending terminal leads create excessive heat and do not efficiently dissipate the heat. Moreover, the sharp edges of the coil are also disadvantageous for insulating the vacuum switch from switches of adjacent phases and against the grounded basic frame of the switch gear.